Frangible fuse cap



Sept 26 1967 D. o. MlsARE 3,344,251

FRANGIBLE FUSE CAP Filed Aug. 26, 1964 United States Patent Oiice 3,344,251 Patented Sept. 26, 1967 3,344,251 FRANGIBLE FUSE CAP Donald 0. Misare, Riverside, Ill., assignor to Joslyn Mfg. and Supply Co., Chicago, Ill., a corporation of Illinois Filed Aug. 26, 1964, Ser. No. 392,119 Claims. (Cl. ZOO- 127) The present invention relates generally to an improved fuse construction, and more specifically to a new and improved frangible fuse cap, particularly adapted for drop out type fused cutouts for use on high voltage electrical transmission lines.

Drop out type fuse circuits are known which are adapted to interrupt both low amperage and high amperage faults equally well, with conventional distribution fuse links. One known type of fuse construction provides a fuse cartridge structure for an open-type fuse cutout. The cartridge includes an open bottom or vent control arranged to provide single venting of the fuse cartridge on low current faults and by providing a rupturable upper cap, the fuse cartridge provides for double venting on faults up fto the maximum interrupting capacity of the cutout. The double venting is obtained by the provision of an expendable, rupturable cap secured to one end of the fuse cartridge. At a predetermined interrupting current, the cap will rupture to vent the cartridge out of both ends.

In operation, if a light overload condition occurs, the usual explosive action takes place with a consequent drop out motion of the fuse tube. The upper end of the fuse tube is completely enclosed. This allows sufficient pressure to be built up in the tube to clear faults of a small magnitude. When operations occur Vfrom a severe short-circuit, the violent explosion, which otherwise would burst the cartridge is #automatically relieved by the vent opening in the top of the cartridge by the rupturing of the frangible section of the expendable cap. This provides double venting of the cartridge from both the top as well as the bottom of the tube. This double venting provides compensating'recoil action which causes a minimum of stress on the cutout through its maximum interrupting capacity.

Although the -cost of an individual cap is not too great, the caps are expendable and are sold in large quantities. The competitive situation requires the caps to be manufactured and sold at the least possible cost. Moreover, the caps must reliably rupture at an adequately predetermined pressure buildup within the fuse cartridge to insure uniform and continuous service of the fuse cartridge. It is desirable to .provide an improved fuse cartridge, and an expendable, -frangble fuse cap for the cartridge, which possesses the above mentioned advanltages.

Accordingly, one object of the present invention is to provide a new and improved frangible fuse cap which possesses the above mentioned advantages.

Another object of lthe present invention is to provide a new and improved frangible fuse cap which may be manufactured at a low cost and which will give reliable and dependable opera-tion.

Yet another object of the present invention is to provide fa new and improved fuse construction .provided with an improved frangible fuse cap, according to the present invention.

Further objects and advantages of the present invention will become apparent as the following description proceeds and the features of novelty which characterize the claims annexed to and forming a part of this specification. invention will 'be pointed out with particularity in the In accordance with these and many other objects of the present invention, there is provided an improved Ifrangible fuse cap for a fuse structure. The fuse cap is adapted for use with a fuse structure formed of a fuse tube or cartridge, open at the bottom and closed at the top. A fuse link capable of interruption upon an a-bnormal amperage fault extends through the fuse tube. The improved frangible fuse cap, according to the present invention, normally, threadingly engages one end of the fuse tube and electrically engages one end of the fuse link to close the upper end of the fuse tube. The lower end of the fuse link is electrically connected to another terminal of the high voltage transmission system. In accordance with the present invention, the frangible fuse cap includes an internally threaded sleeve and an externally threaded disc closing the sleeve. In one embodiment of the invention, the sleeve is of suflicient length so that the disc may 'be threaded intermediate the length of the sleeve -to form fan external barrel `for directing the explosive discharge upon the interruption of the fuse link and preventing scattering thereof.

Advantageously, the frangible fuse caps according to the present invention can be readily and economically manufactured and sold at a minimum cost to provide a highly competitive product. Moreover, the fuse caps will Irupture at the designed pressure with considerable reliability to aiford maximum protection to the fuse cutout.

For a better understanding of the present invention, reference may be had to the accompanying drawing wherein:

FIG, '1 is an elevational View of a fuse assembly, employing an improved frangible fuse cap according to the present invention;

FIG. 2 is an isometric view, partially broken away, of an improved fuse cap according to the present invention;

FIG. 3 is an exploded isometric view of the fuse cap of FIG. 2;

FIG. 4 is an elevational sectional view fragmentarily illustrating the assembly of the components of FIG. 1, and taken along line 4-4 of FIG. l;

FIG. 5 is an elevational sectional view similar to FIG. 4, but illustrating an explosive rupture of the fuse cap upon an abnormally high amperage fault; and

FIG. 6 is a cross-sectional view of a fuse cap according to another embodiment of the present invention.

Referring now to the drawings, and particularly to FIG. 1 thereof, there is illustrated a fuse assembly 10 according to the present invention. The fuse assembly 10 may be of a type known in the art, and, more specifically may be similar to the fuse assembly more fully described in United States Patent 2,862,082 and assigned to the same assignee as the present invention. Briefly, the fuse assembly 10 includes an elongated insulator 12 supported by a suitable bracket 13 from a transmission line superstructure 14 which, in the instant case, is the cross arm of a high voltage tower. IUpper and lower stationary terminal members 15 and 16 are carried at opposite ends of the insulator 12 for connection to the high voltage transmission line. The lower terminal member 16 is provided with a pair of trunnion supports in the form of hook members 18 which are spaced apart and which are provided with overhanging portions 19. The upper terminal member 16 is also provided with a suitable trunnion portion 20. The upper and lower terminal members 15 and 16 are provided with suitable means for connection to a high voltage transmission line.

A drop out fuse structure, generally illustrated at 25 includes a fuse tube or cartridge 26. A downwardly and rearwardly extending arm 27 extends from the lower end of the fuse tube 26 and is provided with a cross trunnion 28 hooked in the hook members 18 to pivotly interconnect the fuse tube 26 to the lower terminal member 16.

The fuse structure 25 further includes an upper terminal 30 adapted to hook or engage within the trunnion portion of the upper terminal member 15 to provide electrical contact with the fuse tube 26.

The fuse assembly lil is provided with a known fuse link 32 having a reduced fusible section 33 adjacent its upper end to provide for rupturing thereof in response to a fault in the power transmission circuit. Additionally, the upper end of the fuse link 32 is secured to a disc shaped head 34 resting on the terminal 30. A washer 35 of brass or other electrically conductive material may be interposed between the head 34 and the terminal 30. The lower end of the fuse link 32 extends through the open lower end of the fuse tube 26 and is secured to suitable spring structure 37 adapted to snap the fuse link 32 out of the tube 26 upon rupture of the fuse link 32.

In order to retain the upper end of the fuse link 32, the terminal 30 is provided with an upper threaded portion 38 having suitable external threads to receive a closure cap 40, according to the present invention. As illustrated in FIGS. 2 and 3, the closure cap 40 is formed of an internally threaded sleeve 41, knurled on the outside. A thin externally threaded disc 42 is threaded into the sleeve 41 to form the closure cap 40. In the illustrated embodiment, the closure cap 40, after assembly of the sleeve and disc, is dip coated in silver to meet the necessary electrical standards. The dip coating of thin silver serves the additional purpose of sealing between the threads of the disc 42 and the sleeve 41 to form a hermetically sealed closure cap 40.

yIn view of the thin nature of the disc 42, and the limited number of threads thereof which can be in engagement with the sleeve 41, the disc 42 will rupture at its threaded edges in the event of an abnormally high current fault. More specifically, it will bel understood that if a light overload condition occurs, the usual expulsion action takes place in the tube 26 with a consequent drop out motion of the fuse tube. The upper end of the fuse tube 26 is completely enclosed by the closure cap 40. Suicient pressure therefore will build up within the tube 26 to clear the faults of small magnitudes. However, when the operations occur from a severe short-circuit, a violent explosion can occur which would otherwise burst the tube 26. However, the tube 26 is automatically relieved by the rupture of the frangible disc 42 in the closure cap 40. This vents the tube 26 from both its upper and lower end and immediately changes the tube characteristic from a single vented device to a dual vented tube.

Since the caps 40 are expendable, and since the power transmission component business is highly competitive, the closure cap 40, according to the present invention, provides a structure which may be manufactured and assembled at low cost and may be competitively sold in the commercial market. Moreover, the rupture pressure of the cap can be readily varied by altering the thickness of the disc 42 and thereby changing the number of threads of the disc 42 which are in engagement with sleeve 41. The internally threaded sleeve 41 serves the dual function of electrically securing the disc shaped head 34 of the fuse link 32 to the terminal member 30 through threaded engagement between the closure cap 40 and the terminal 30, and additionally provides the internally threaded portion to receive the disc 42.

FIG. 6 illustrates an embodiment of a closure cap 50 which is effective to direct the explosive discharge from the tube and prevent scattering thereof upon explosive interruption of the fuse link 32. More specifically, the closure cap 50 includes an internally threaded elongated sleeve 51, knurled on the outside. A frangible disc 52 of predetermined desired thickness is threaded into the sleeve 51 intermediate the length of the sleeve. In this manner, there is provided a short barrel 53 above the disc 52, externally of the fuse tube 26, which is effective to direct the firing of the disc 52 and to control the scattering of the explosive discharge from the tube 26.

Although the present invention has been described b'y reference to two embodiments thereof, it will be apparent that numerous other modifications and embodiments will be devised by those skilled in the art which will fall within the true spirit and scope of the present invention.

What is claimed as new and desired to be secured by Letters Patent of the United States is:

1. A fuse construction comprising a fuse tube having a terminal structure at one end; a fuse link capable of interruptions upon abnormal amperage faults and extending through the fuse tube and provided with `a disc shaped head at said one end of said tube; and a cap normally threadingly engaging the terminal to retain said head and to close said one end of said fuse tube; said cap including an internally threaded sleeve and an externally threaded thin disc closing said sleeve and thread ingly received in said sleeve and rupturable along its threaded edges when a predetermined pressure is developed in said fuse tube upon explosive interruption of said fuse link in response to high amperage faults.

2. A fuse construction as set forth in claim 1 above wherein said disc is `of predetermined thickness to provide rupture thereof at predetermined pressure.

3. A fuse construction as set forth in claim 2 above wherein said cap is metallic coated thereby hermetically sealing said disc and sleeve.

4. A fuse construction as set forth in claim 3 above wherein said metallic coating is of silver.

5. A fuse construction as set forth in claim 2 above wherein said disc is positioned intermediate the length of said sleeve to form an external barrel for directing the explosive discharge and preventing scattering thereof upon explosive interruption of said fuse link.

6. A rupturable cap for use on a fuse tube of the type open at one end and having a fuse link extending therethrough said cap comprising an internally threaded sleeve closed with an externally threaded thin disc threadedly received therein said disc being adapted to rupture at its threaded edges upon excessive pressure buildup in a fuse tube.

7. A cap as set forth in claim 6 above wherein said disc is of predetermined thickness to provide rupture thereof at preselected pressure.

8. A cap as set forth in claim 6 above land additionally including a metallic coating effective to hermetically seal said disc and sleeve.

9. A cap as set forth in claim y8 above wherein said coating is silver.

10. A cap as set forth in claim 6 above wherein said disc is positioned intermediate the length of said sleeve.

References Cited UNITED STATES PATENTS 1,987,543 1/1935 West et al 20G-l2() 2,070,315 2/ 1937 Rawlins et al. 20G-127 2,583,440 l/l952 Oxley et al 20G-120 X 2,846,544 8/l958 Wood 20G-120 3,079,861 3/ 1963 Charrin 102--20 BERNARD A. GILHEANY, Primary Examiner, I-I. GIALSON, Assistant Examiner, 

1. A FUSE CONSTRUCTION COMPRISING A FUSE TUBE HAVING A TERMINAL STRUCTURE AT ONE END; A FUSE LINK CAPABLE OF INTERRUPTIONS UPON ABNORMAL AMPERAGE FAULTS AND EXTENDING THROUGH THE FUSE TUBE AND PROVIDED WITH A DISC SHAPED HEAD AT SAID ONE END OF SAID TUBE; AND A CAP NORMALLY THREADINGLY ENGAGING THE TERMINAL TO RETAIN SAID HEAD AND TO CLOSE SAID ONE END OF SAID FUSE TUBE; SAID CAP INCLUDING AN INTERNALLY THREADED SLEEVE AND AN EXTERNALLY THREADED THIN DISC CLOSING SAID SLEEVE AND THREADINGLY RECEIVED IN SAID SLEEVE AND RUPTURNABLE ALONG ITS THREADED EDGES WHEN A PREDETERMINED PRESSURE IS DEVELOPED IN SAID FUSE TUBE UPON EXPLOSIVE INTERRUPTION OF SAID FUSE LINK IN RESPONSE TO HIGH AMPERAGE FAULTS. 